Method for producing a hollow molded article with a filling of foamed plastic thermal insulation, and the article produced thereby

ABSTRACT

The molded shell of an article, while still warm from being molded, and while remaining within the mold or fixture in which it has been created, for instance by blow-molding of a parison of polyolefin plastic material into contact with the mold walls, is filled with a fluid, settable foaming plastic material, for instance polyurethane. This may be done by injecting the foaming mixture directly into the cavity of the shell. In this manner time, labor and materials are saved, and the resulting product is characterized by better adhesion of the foamed core to the internal wall surface of the shell.

This is a continuation of application Ser. No. 443,789, filed Nov. 22,1982, now U.S. Pat. No. 4,546,899.

BACKGROUND OF THE INVENTION

A variety of structural parts and complete articles is conventionallymade by a process wherein the shell of the article is first blow-moldedor similarly cast or molded. Sometimes the shell is made in two or morecomplementary sections which are then seamed together about aperimetrical rim e.g. by thermal bonding, acoustic welding or by anadhesive, in order to define an internal cavity. Such a process isconventionally used, even though it is obviously cumbersome, because itgives the manufacturer a chance to flame-etch on the sections thesurfaces that will become the internal surfaces of the shell cavity, forincreasing the adhesion of the core foam thereto. Then, after this shellis fabricated, set or cooled and removed from the mold or fixture, afoamed plastic composition is injected through an opening purposely madeor left filling the cavity with foam which sets. Finally, the opening isplugged completing the creation of an article which has a typicallydense, tough, cleanable skin with a lightweight core which has the bonusof being thermally insulative. Typical uses for such articles are asbodies and lids of picnic chests, coolers, hospital trays, enclosuresfor hot or cold casseroles of food, containers for chemical, medical,biological and pharmaceutical specimens and products, refrigeratorcabinet boxes and doors, food service containers and enclosures for foodservice containers, and the like.

A typical thermoplastic material used to make the shell of such articlesis polyethylene, polypropylene or the like.

A typical foamed plastic core is made of polyurethane by using acommercially available Gusmer Gun in accordance with its manufacturer'sinstructions. (Gusmer Corporation, Route 18 and Spring Valley Road, OldBridge, N.J. 08857). In a standard Gusmer Gun system, as shown in FIG. 1of the drawings, pressurized air is supplied at 10 through a regulator12 and valve 14 to an air motor 16 the piston rod 18 of which is yokedat 20 to the piston rods 22 of the piston-type proportionating pumps 24,26 respectively for resin and activator. The pumps 24, 26 in turn havetheir suction sides respectively communicated to supply drums 28, 30 ofresin and activator. The pressure sides of pumps 24, 26 are communicatedthrough respective heaters 32, 34 to respective inlet ports of a mixingand ejecting gun 36. Within the gun 36 the properly proportioned streamsof heated resin and activator come together in a mixing chamber 38 fromthe front of which the foamable mixture is ejected through a nozzle (notseen in this rear view). Typically in the Gusmer Gun system, the resintank contains a prepolymer of polyisocyanate, polyether polyol and asurfactant, and the activator tank contains catalysts and water. Systemsof this general type have become well-known over the years and arerather completely described in the readily available trade literature,complete with exemplification. See, for instance T. H. Ferrigno, RigidPlastics Foams, Reinhold Publishing Corporation, New York 1963, entiretext, and especially pages 53-72 and 118-123; and "Polyurethans",Encyclopedia of Polymer Science and Technology, Interscience PublishersNew York 1969, especially volume 11, pages 537-548.

It is not for its thermal insulating properties alone that rigid plasticfoam is used for void-filling of article shells. A very importantdesired function of the foam is, by adherence to the interior walls ofthe shell, unification and rigidification of the article as a whole,i.e. to give the article structural strength and a feel of integrity,though light in weight.

The prior art article and method have been subject to drawbacks whichhave gone unrelieved for a number of years. Particularly, it istime-consuming to hold a hollow molded shell in the mold or fixturewhile waiting for it to cool, cure or set sufficiently to be removed andremain free-standing without drooping, wilting, warping or otherwisebecoming distorted, and then to fill the shell cavity with foamingplastic in a separate operation. The two step operation is unduly laborintensive, and may call for additional capital investment, e.g. for jigsor fixtures to hold the shells while they are being foam-filled, inorder to prevent or minimize warpage and other distortion due to localover-filling with foam.

In addition, the prior art process is believed to consume moreingredients than theoretically necessary in manufacture of the foamfilling, since an excess customarily is used in an attempt to insurethat the entire void within the hollow shell is filled with foamedplastic. Even so, it is a troublesome artifact of use of the prior artmethod, especially on articles such as hospital trays which will be putthrough heat cycles, e.g. in the course of being washed in a dishwasher,that the shell balloons or buckles away from the foamed core fairlyearly in the life of the article. The article then has an unwanted feel;it no longer seems to be a structurally integral article, but one with aflexible skin over a definite internal body. Indeed the article maygive-off a crackling, rattling, grating sound during use, as its shellcontacts and comes away from the core. Needless to say, to the extentthat the core is separated from the shell, the desirable structuralstrength is degraded.

SUMMARY OF THE INVENTION

The molded shell of an article, while still warm from being molded, andwhile remaining within the mold or fixture in which it has been created,for instance by blow-molding of a parison of polyolefin plastic materialinto contact with the mold walls, is filled with a fluid, settablefoaming plastic material, for instance polyurethane. This may be done byinjecting the foaming mixture directly into the cavity of the shell. Inthis manner time, labor and materials are saved, and the resultingproduct is characterized by better adhesion of the foamed core to theinternal wall surface of the shell.

The principles of the invention will be further discussed with referenceto the drawings wherein a preferred embodiment is shown. The specificsillustrated in the drawings are intended to exemplify, rather thanlimit, aspects of the invention as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings

FIG. 1 is a diagrammatic view, with legends, of a commercially availableprior art system for storing, supplying and mixing the ingredients of anin situ foaming void-filling plastic material such a polyrethane, andfor ejecting the foaming composition from the nozzle of a gun;

FIG. 2 is a diagrammatic view of a parison for the article shell beingconventionally extruded into place between the mold-halves of a blowmolding machine;

FIG. 3 is a diagrammatic view of a stage at which the mold halves haveclosed onto the parison defining a shell internal cavity which is beingconventionally enlarged by inflating the plastic into intimacy with themold cavity surfaces;

FIG. 4 is a diagrammatic view of a stage at which the distinguishingfeatures of the present invention become more evident, in that here aninjector is shown being used to fill the entire cavity of thejust-molded article shell with foaming plastic while the article shellremains hot and in place within the mold;

FIG. 5 is a diagrammatic view illustrating completion of the step whichis shown being initiated in FIG. 4; and

FIG. 6 is a diagrammatic cross-sectional view of a completed articleproduced by the process and with the apparatus of the present invention,the foam filling having set and remaining strongly adhered to theinternal surface of the shell.

DETAILED DESCRIPTION

In FIG. 2, a standard blow-molding machine is illustrated in a generalway by the showing of opposed mold halves 40, 42 which are movablehorizontally toward and away from one another to close and open up amold cavity defined by the internal surfaces 44.

(In the instance depicted, the mold cavity, shown opened-up, is designedfor forming the shell of a tray article such as is used by hospitals andfood service suppliers to airlines and the like, for keeping hotindividual containers of food which are placed in the respectiveupwardly open recesses of a lower tray and covered by the respectivedownwardly open recesses of an upper, like tray. Thus a plurality ofmeals can be kept hot by stacking a plurality of such trays one on topof the other with containers of heated food enclosed in the cooperatingrecesses between vertically adjacent twos of the trays in the stack. forserving the meals, the trays are simply de-stacked, exposing theindividual containers which thus have been kept hot.)

The mold cavity surfaces 44 are perimetrically bounded by respectiverims 46 which tend to engage to clamp the parison in the mold as themold closes, in order to define a closed volume that is subject to beinginflated.

The conventional blow-molder is further shown being conventionallyserved by an extruding head 48 for extruding a tubular parison 50 ofplastic into the space between the mold halves each time the mold cavityopens up.

At the subsequent stage depicted in FIG. 3, the mold halves have beenclosed about the parison, defining a mold cavity and defining of theparison a closed volume that is subject to being inflated. Inflation istypically accomplished using a hollow needle 52 mounted in a bore 54 inone of the mold halves, on an extender/retractor cylinder arrangement56. The needle 52 and the arrangement 56 are connected to a supply ofcompressed air. After the mold halves have closed creating the moldcavity, compressed air is communicated to the arrangement 56 whichextends the needle in the bore 54 to such an extent that it pierces theclamped parison and causes the hollow needle tip 58 to become located inthe internal void 60 of the clamped parison. Then, compressed air isintroduced into the internal void inflating the clamped parison againstthe mold cavity surface to define the external size and shape of thearticle shell 62. The supply of compressed air then is cut off and theneedle retracts. The puncture eventually substantially recloses and thescar is generally unnoticeable to the casual user of the finishedproduct. Although one inflater 52-58 is depicted, in actual practice, aplurality of such inflaters which are distributed about the mold may beused, such practice being conventional.

(The conventional inflation device 52-58 is simply not depicted in FIG.2.)

The conventional inflation device 52-58 that is depicted is but oneexample of the many generally similar sorts of such devices as are incommon use in the blow molding industry. In a common variation theinflation probe is aligned on the parting line plane of the mold, sothat it need not be thrust to pierce and then withdrawn after inflation,but merely remain stationary.

All that has been described so far with regard to FIGS. 1-3 is utterlyconventional and typical in everyday commercial practice. Differencesattendant to practicing the principles of the present invention firstbecome evident with regard to FIG. 4.

In order to practice the principles of the present invention, the moldor equivalent fixture 40, 42 is modified by providing another bore 64therein intersecting with the mold cavity at a place corresponding to aninconspicuous site on the exterior of the article shell 62.

The ejector nozzle of the mixing and ejecting gun 36 of FIG. 1, isfitted with a hollow needle 68, which, if the bore 64 is not aligned onthe parting line plane of the mold, is mounted on an extender/retractorcylinder arrangement 70 (like the one 56). The gun 36 and/or thearrangement 70 is mounted to the respective mold half. The arrangement70 is connected to a source of compressed air for extending andretracting the hollow needle through the bore 64 into and out of themold cavity. As with the needle 52, the site selected for theintersection of the bore 64 with the mold cavity is selected such thatthe small scar made by use of the needle to puncture and then withdrawfrom the article shell 62 will generally go unnoticed by the casual userof the finished article.

(The bore 64 and apparatus 68, 70 are simply not depicted in FIGS. 2 and3.)

The gun 36 remains connected to an otherwise unmodified foamed plasticproducing system such as is depicted in FIG. 1.

Accordingly, after the tubular parison of a selected thermoplasticmaterial is extruded between the mold halves (FIG. 2) and the mold isclosed and a slight pre-blow is applied through the air needle to trapenough air within the parison-enclosed space to hold the parison wallsapart, and further air is introduced while vacuum is conventionallydrawn through a plurality of holes (not shown) through the mold,conforming the warm thermoplastic against the mold cavity wall surfaceand thus defining the article shell FIG. 3, the air supply to the airneedle or air needles is cut off. Any air needles not on the moldparting line plane are withdrawing, the sites where they had puncturedthe thermoplastic shell wall temporarily serving as vents through whichair trapped within the article shell can flow out or be expelled.

Preferably, the plastic foam injecting needle 68 is extended to piercethe article shell at a moment in time when the article shell is stillbeing inflated by the air nozzles and the article shell is still beingpulled against the mold cavity wall surface by vacuum drawn through themold wall, in order to prevent the thrusting, piercing action fromlocally distorting the article shell.

Once the article shell inflation air pressure is reduced by venting, butwithout further delay, the apparatus of FIG. 1 is operated to injectfoaming plastic through the needle(s) 68 into the internal cavity 72 ofthe article shell. The length of time that the plastic injectoroperates, and the amount of plastic material injected depends on thevolume of the cavity 72. As the injected plastic material foams andexpands, the rigidifying foam pushes the wall of the article shell moretightly against the mold cavity surface. The conventionally cooled wallsof the mold cool the thermoplastic of the shell while within the nowfoam-filled cavity 72 of the article shell, the foamed plastic cures andbecomes generally rigid or solidified in its cellular condition (FIG.5).

Finally, the mold is opened and the completed article 74 is removed(FIG. 6).

Having made the same products both ways, i.e. by the conventional methodwhere the void-filling foam is installed in a separate step after thecooled article shell has been removed from the blow-molding machine, andby the method according to the present invention as describedhereinabove, the inventor has found that the method of the presentinvention provides certain advantages in addition to a reduction in thetime and labor needed to produce each article. Surprisingly, it has beenfound that approximately 30 percent less, by weight, of foamable plasticmaterial needs to be injected into the article shell in order to producea fully acceptable article having substantially equal thermal insulatingproperties.

Another important advantage, is that adhesion between the externalsurface of the set foamed plastic core and the internal cavity wall ofthe article shell is substantially improved in comparison with the priorart article. This is considered to be very important, because warpingand buckling of the shell away from the core during autoclaving orcommercial dishwashing of the article is virtually eliminated as aproblem. The improvement in adhesion is believed to be accomplished whenusing the process of the invention because of the introduction of thefoaming plastic composition into the void within the article shell whilethe article shell is still very hot, and is extensively confined againstany expansion.

The principles of the present invention are further illustrated withreference to the following example, which relates to manufacturing of afood service tray of the type shown in FIGS. 2-6, using the method andapparatus of the present invention as described herein. All of thefollowing details should be understood as being simply illustrative andnot as limiting the scope or applicability of the present invention.

Make and Model of Blow Molding Machine

Impco B-30

Weight of Article Shell

750 grams

Average Wall Thickness of Article Shell

0.070

Composition of Article Shell (a) Trade Name (b) Chemical Name

polypropylene

polypropylene

Amount of Time Delay Between When Inflating Air is Cut-Off and GusmerGun is Turned On

10 seconds or less

Average Temperature of Article Shell Internal Cavity Wall SurfaceTemperature At Time Injection of Foamable Composition is Begun

350 to 400 degrees

Average Temperature of Foamable Composition as Injected

70 to 75 max

Composition of Resin and Activator Constituents of Foamable Composition(a) Trade Names (b) Chemical Names

(a) Freeman isocyanate

(b) Chempol 32-1973

Weight Ratio of Resin to Activator Constituents as Injected

Equal by weight

Volume of Cavity of Article Shell

1500 cc

Weight of Foaming Composition Injected Into Cavity

100 grams

Amount of Time Taken for Injecting the Foaming Composition

4 to 6 seconds

Amount of Time That the Article Remains in the Mold After Injection ofthe Foaming Composition Has Been Completed

60 seconds

Surface Temperature of the Mold Cavity at the Time the Mold Closes onthe Parison

50 degrees approximately

Surface Temperature of the Mold Cavity at the Time the Mold Opens toRelease the Finished Article

50 degrees approximately

It should now be apparent that the apparatus and method for producingmolded hollow article with filling of foamed plastic thermal insulation,and article produced thereby as described hereinabove, possesses each ofthe attributes set forth in the specification under the heading "Summaryof the Invention" hereinbefore. Because it can be modified to someextent without departing from the principles thereof as they have beenoutlined and in this specification, the present invention should beunderstood as encompassing all such modifications as are within thespirit and scope of the following claims.

What is claimed is:
 1. A method for producing a molded hollow articlewith filling of foamed plastic thermal insulating material,comprising:inserting a hot precursor, made of polyolefin, for apolyolefin article shell into a relatively cool mold having a moldcavity with an internal molding surface therein; conforming the hotprecursor against the internal molding surface to define an articleshell having an internal cavity bounded by an internal surface of thearticle shell; introducing through the mold and through the articleshell into the internal cavity of the article shell, a quantum ofactivated, foamable, settable polyurethane thermal insulation materialwhile said article shell remains hot, so that as the article shell isbeing cooled from an elevated temperature by contact with the mold, thethermal insulation material foams, fills the internal cavity of thearticle shell, adhering to the internal surface of the article shell,and sets to form a foamed core of polyurethane that is extensivelyadhered to the article shell to define an article; and removing thearticle from the mold.
 2. The method of claim 1, wherein:the insertingstep is performed by opening said mold, extruding a generally tubularparison within the open mold, and closing the mold onto the parison toperimetrically trappingly ring a portion of the parison within the moldcavity.
 3. The method of claim 2, wherein:the conforming step isperformed, at least in part by inflation of said parison portion.
 4. Themethod of claim 3, wherein:the conforming step further includes drawinga vacuum through the mold externally of the parison portion.
 5. Themethod of claim 1, wherein:the introducing step comprises piercing thearticle shell with a hollow needle and injecting said activated,foamable, settable polyurethane thermal insulation material through thehollow needle into the article shell.
 6. The method of claim 5,wherein:the activated, foamable, settable polyurethane thermalinsulation material comprises a mixture of an isocyanate, a polyetherpolyol, a catalyst and a blowing agent.
 7. An article produced by theprocess of claim
 1. 8. A molded hollow article with filling of foamedplastic thermal insulating material produced by the process of claim 1.